Biodegradable polyesteramides are known in the art, in particular α-amino acid-diol-diester based polyesteramides (PEA) are known from G. Tsitlanadze, et al. J. Biomater. Sci. Polym. Edn. (2004) 15:1-24. These polyesteramides provide a variety of physical and mechanical properties as well as biodegradable profiles which can be adjusted by varying three components in the building blocks during their synthesis: naturally occurring amino acids and, therefore, hydrophobic alpha-amino acids, non-toxic fatty diols and aliphatic dicarboxylic acids.
WO2002/18477 specifically refers to alpha-amino acid-diol-diester based polyesteramides (PEA) copolymers of formula I, further referred to as PEA-I,
wherein:                m varies from 0.1 to 0.9; p varies from 0.9 to 0.1; n varies from 50 to150;        each R1 is independently (C1-C20)alkylene;        each R2 is independently hydrogen or (C6-C10)aryl(C1-C6)alkyl;        each R3 is independently hydrogen, (C1-C6) alkyl, (C2-C6)alkenyl, (C2-C6)alkynyl, or (C6-C10)aryl(C1-C6)alkyl; and        each R4 is independently (C2-C20)alkylene.        
PEA-I is a random copolymer comprising m units build upon alpha-amino acids, diols and an aliphatic dicarboxylic acids, which are copolymerized with p units build upon an aliphatic dicarboxylic acid and L-lysine. The R2 in the amino acid L-lysine is either H (hereinafter referred to PEA-I-H) or a (C6-C10)aryl(C1-C6)alkyl from which benzyl is the most preferred. In case that the R2 in L-lysine of PEA-I comprises benzyl it is further referred to as (PEA-I-Bz).
It has been recognized that PEA-I-H shows high swelling profiles which results in a fast degradation and a quick burst release of bioactive agents in approximately 24-48 hours. These properties have reduced the attention of PEA-I-H polymers as materials with potential in drug delivery. It has also been recognized that PEA-I-H enzymatically degrades very fast, for example in vitro it completely degrades in 1 week. On the other hand it has been recognized that PEA-I-Bz provides a more sustained release of bioactive agents over a prolonged period of time. Moreover it shows minor if any swelling properties. PEA-I-Bz enzymatically degrades slowly and the in-vivo degradation of the polymer strongly depends of the administration site, tissue response and health status of the studied model. However, PEA-I-Bz lacks the ability to degrade hydrolytically in absence of enzymes which could result in too slow or even non complete degradation of the polymer.
The same disadvantages appear to be true for another type of prior art PEA random co-polymers according to Formula II which comprise at least two linear saturated or unsaturated aliphatic diol residues into two bis-(a amino acid)-based diol diesters. These copolymers are for example disclosed in WO2008/0299174.

In a preferred embodiment of above polyesteramide co-polymer m varies from 0.01 to 0.99; p varies from 0.2 to 3 and q varies from 0.10 to 1.00 whereby n is 5 to 100; R1 is —(CH2)8; R3 and R4 in the backbone units m and p is leucine, —R5 is hexane, and R6 is a bicyclic-fragments of 1,4:3,6-dianhydrohexitols of structural formula (III);
R7 may be chosen from H or a benzyl group and R8 is —(CH2)4-.If R7 is H the polymer is further indicated as PEA-III-H, if R7 is benzyl, the polymer is further indicated as PEA-III-Bz.